Inflammatoire fenotypes van chemisch-geïnduceerd astma

Asthma is a heterogeneous airway disease, characterized by chronic airway inflammation, variable airway remodeling, reversible airway obstruction and non-specific airway hyperreactivity (AHR). The respiratory symptoms include wheezing, shortness of breath, chest tightness and cough. In adults, 9-15% of all asthma cases are attributable to exposure to agents on the workplace, called occupational asthma (OA). OA is therefore one of the most common forms of occupational lung disease in many industrialized countries. Based on the presence or absence of an asymptomatic latency period, OA can be divided into two phenotypes. First, immunological OA appears after a latency period of exposure (months to years) necessary for acquiring immune sensitization to the causal agent. This phenotype of OA encompasses OA induced by an immunoglobulin (Ig)E mediated mechanism (most high- and some low- molecular weight agents), and OA in which the IgE mechanism has not been consistently demonstrated (low molecular weight agents such as western red cedar, acrylates and isocyanates). Second, non-immunological OA, in which asthma occurs after an acute exposure to high concentrations of an irritant, without a latency period, termed irritant-induced asthma. Diisocyanates are reactive chemicals, used in the polyurethane industry for the manufacture of flexible and rigid foams, fibers, paints and varnishes. They are one of the most important causes of OA. Low airborne levels of diisocyanates, even below the established permissible exposure level, can trigger asthmatic reactions in individuals sensitized to diisocyanates. An important difference between protein-induced allergic asthma and chemical-induced asthma, is that the chemicals first need to bind to endogenous proteins before they become recognizable by the immune system resulting in a different, not yet fully delineated mechanism of action. In this doctoral thesis, we used an established acute mouse model of chemical-induced asthma. This model consists of a dermal sensitization phase followed by a single airway exposure. This acute exposure model results in AHR and airway inflammation that is mainly dominated by neutrophils in conjunction with the presence of eosinophils. This acute mouse model has been suitable to validate chemicals for their asthmatic potency and to study several key players in chemical-induced asthma. However, due to the short-term exposure time, there are some limitations in this model such as the absence of a robust lung inflammation and airway remodeling. Therefore, we developed a chronic and a sub-chronic mouse model of chemical-induced asthma. Study of the cross-reactivity between MDI and TDI In the first part of this thesis, we optimized the acute mouse model using 2,4-toluene diisocyanate in C57Bl/6 mice, and validated the sensitization and asthmogenic potency of 4,4-methylene diphenyl diisocyanate (MDI). Both TDI and MDI were potent sensitizers and asthmogens in the C57Bl/6 mice. However MDI was, compared to TDI, a somewhat weaker dermal sensitizer and asthmogen. Additionally, we investigated whether there is cross-reactivity between TDI and MDI. We studied the cross-reactivity between TDI and MDI by dermally sensitizing mice with TDI followed by an airway challenge with MDI and vice versa. In this acute model, with a single airway challenge, we did not observed cross-reactivity between TDI and MDI. Development of a chronic and sub-chronic mouse model and study the presence of dendritic cells Development of a chronic intranasal mouse model In the second part of this thesis, we attempted to obtain a severe chemical-induced asthmatic phenotype with pronounced lung inflammation and airway remodeling. Chronic intranasal exposure (daily intranasal instillation exposure - 5 days a week - for five consecutive weeks) resulted in a predominant T helper (Th1) systemic immune response, without AHR nor recruitment of inflammatory and dendritic cells (DC). By adding prior dermal sensitization, intranasal exposures resulted in a predominant systemic Th2 immune response accompanied with AHR. Still, the AHR was not accompanied with airway inflammation nor recruitment of DC in the lung, mimicking the clinically relevant paucigranulocytic phenotype of asthma. As a conclusion, dermal contact with TDI prior to long-term respiratory exposures determines the outcome of systemic immune sensitization and the presence of AHR. Development of a sub-chronic oropharyngeal mouse model Since we were unable to find airway inflammation in the chronic intranasal mouse model, the last part of this thesis focused on the development of a mouse model using an oropharyngeal instillation technique to expose the lower airways to TDI. Multiple oropharyngeal TDI exposures resulted in airway inflammation accompanied with DC recruitment to the lung, which is indicative of the initiation of an adaptive immune response in the lung. However, the type of inflammation is shaped by the route of exposure. Without skin exposure the inflammation is dominated by mainly neutrophils, which is indicative for irritant-induced inflammation, while prior skin sensitization with TDI resulted in an eosinophilic airway inflammation accompanied with AHR, which is indicative for an immune-mediated inflammatory phenotype of asthma. As a conclusion, DC are recruited to the lungs in the presence of inflammation, and pre-dermal contact with TDI determines the type of lung inflammation (eosinophilic versus neutrophilic) and the presence of AHR.status: publishe